Urban Stormwater Runoff

What affects urban stormwater runoff

Nutrients, pollutants and sediment collected in stormwater from urban areas fringing the lakes (‘urban stormwater runoff’) can be highly concentrated inputs to the lakes.

The diagram on the left shows 4 actions/events common to a typical household that contribute to urban stormwater runoff.

1. Fertiliser (poison bottle) is sprayed on grass lawns. When it rains, excess nutrients from the fertiliser flow into the drain and into the lake.
2. A car is being washed on the concrete driveway using town water. Any detergent used, as well as any petrochemicals on the driveway from car exhaust, are collected in the runoff and flow directly into the drain and into the lake.
3. Green waste (leaves, sticks, dirt) is left on the concrete driveway and in road side gutters. When it rains, the runoff collects leaves and sediment which flows into the drain and into the lake.
4. During a rain event, no rain water is collected. Instead, the runoff collects nutrients, pollutants and dust/sediment from the roof, driveway, lawn and gutters, all of which flow into the drain and into the lake.

The diagram on the right shows 4 ways that a typical household can reduce the amount of nutrients, pollutants and sediment flowing into the lakes.

1. Instead of using fertiliser on your lawns try using compost, such as ‘worm waste’ from a worm composting system, to fertilise your lawn. If using fertiliser, only use the recommended amount or less.
2. If possible wash your car on a lawn or grass verge, using rainwater. Washing your car on a the lawn or grass allows the soil/ sand substrate filter out some or all of the nutrients before they reach the lakes (via groundwater seepage). Or, take your car to a Car Wash business where waste water is recycled and reused.
3. Collect green waste from your property and use it for compost. Do not blow leaves down the drain. Collect leaves from the gutters so they don’t end up in the lake where they contribute to the nutrient load.
4. Install rainwater tanks. All runoff from the roof is collected in the tanks and does not contribute to stormwater flowing into the lake. Use rainwater to water your lawn and garden, and for washing your car on the lawn.

Council have installed many stormwater quality improvement devices (SQID) such as Gross Pollutant Traps in the catchment. Such devices can become quickly overwhelmed and blocked by the quantity of trapped pollutants. Reducing the amount of sediment /leaves /rubbish that enters the drain in the first place will allow SQID to be more effective at reducing the pollution that enters the lakes.

Did you know? urban stormwater runoff becomes trapped in the near-shore zone, particularly in those areas protected from wind and waves. This enrichment of the near-shore zone by urban runoff exacerbates the poor water quality, the frequency of macroalgal blooms and the formation of organic black ooze in the sediment. Smells awful and doesn’t look very good either.